1. Field of the Invention
The present invention relates to a method of effectively configuring an overlay 1:N data transmission tree capable of transmitting effective group data to mobile hosts (MHs) in a wireless local area network (WLAN) environment, and more particularly, to a method of configuring a data transmission tree enabling effective multicast communication even in a WLAN environment without changing existing Internet infrastructures, using a one-to-one communication method (unicast method) in a current wired and/or wireless environment, and a multicast agent therefor.
2. Description of the Related Art
Multicast technology allows a transmitter to efficiently use the resources and bandwidth of a transmission node when the transmitter transmits the same data to a plurality of receivers at the same time, and is the most suitable mechanism for transferring application data for group communication methods.
However, up to now multicast technology (or internet protocol (IP) multicast) has been only partially enabled, and only for testbeds, some intranets, school networks, or experimental networks. The reasons why the multicast is not fully supported include the cost required for replacing all routers currently in the Internet with multicast-enabled routers, and technical problems, including address allocation, multicast routing protocols, and hardware state management mechanisms. These problems are serious in a wired network environment but more so in a wireless network environment. This is because when a mobile host (MH) communicating in a wireless local area network (WLAN) environment changes the WLAN, a data transmission path from a transmitter to the MH passing through wired and/or wireless environments must be modified.
First, the problem of IP multicast in an ordinary wired network environment will be explained.
An example of a load problem of an IP multicast router is that a current IP multicast backbone router must be heavily loaded in order to manage a routing table for members frequently subscribing to and/or withdrawing from a group. However, actually, an IP multicast network is a dynamic network which frequently changes as applications start and end, unlike a unicast fixed IP network. That is, to generate an IP multicast data transmission path, an application subscribes to a session which is publicly noticed in advance (group address, port number, digital content, etc.), and according to the subscription a data transmission and reception path is generated.
Next, the problem of IP multicast in an ordinary wireless network will be explained.
MHs in a wireless network can freely subscribe to or withdraw from a group as terminal nodes in a wired network. In addition, even a node subscribing to a group communication causes a handover by traveling through WLAN segments.
Accordingly, there is a recent demand for enabling multicast by using programs at an application layer without replacing Internet equipment.
According to this method, a non-multicast area for which a multicast router is not directly connected to a multicast backbone is connected using tunneling through a virtual multicast router, thereby enabling IP multicast between a transmitter and receivers. When this method is employed, ordinary personal computer (PC) users can access a virtual multicast router and use IP multicast. However, the address collision problem of IP multicast or the load problem to manage multicast routing state information in each multicast device cannot be essentially solved. Furthermore, since the tunneling technique for connecting the non-multicast area considers only tunneling with a short-distance hop, a bottleneck can occur in an intermediate node connecting the tunneling.